In typical sampling calorimeters, the amount of light created by an incoming particle, such as a gamma ray from PET, or a high-energy electron from an accelerator beam, is proportional to the energy of the particle. Typically, the light is then turned into an electrical signal whose total charge is proportional to the amount of light.
The detection of energetic radiation such as gamma rays, neutrons, and charged particles depends on their interaction with matter, in particular the energy the radiation deposits inside material. For energetic radiation, the amount of material needed in the path of the particle for a measurement of the energy of the particle (gamma, neutron, or charged) depends on the energy and type of the particle. Detectors that measure the total energy of particles typically contain all the energy deposited along the path of the particle, necessitating a detector with substantial depth, and therefore a large volume. For detectors that cover a large area, the requirement of substantial depth to contain all the energy results in a large detector mass, and typically thus a large cost.
Medical imaging cameras such as those used in Positron Emission Tomography (PET), Single photon emission computed tomography (SPECT, or less commonly, SPET), Scintigraphy, or other nuclear medicine tomographic imaging techniques use dense crystals or glass to measure the position and energy of gamma rays emerging from the subject, allowing reconstruction of tumors and other pathologies. The spatial resolution is typically limited by the position resolution of the detector arrays, scattering, blurring due to depth-of-interaction uncertainty, and limited signal-to-noise due to the 2-dimensional nature of the recorded information.
Sampling calorimeter radiation detectors, commonly called calorimeters, are also used for energy measurements of high-energy particles such as electrons, photons, protons, neutrons, and mesons. However both spatial and time resolutions are typically limited by the granularity of the construction geometry, which is constrained by the problem of getting the light produced by the radiation inside the detector out to the photo-detectors and the electronics.